1. Field of the Invention
This invention relates to an information signal processing device for processing an information signal and more particularly to a device arranged to process an information signal by using a delay element.
2. Description of the Related Art
Heretofore, a delay element called a CCD (charge-coupled device) has popularly been employed as means for delaying, for example, an analog video signal. In the case of a video tape recorder, the CCD is used for circuit elements such as a dropout compensation circuit which is well known and a comb filter which separates a luminance signal and a chrominance signal from a video signal. The CCD has steps the number of which varies according to the delay time, and is arranged to sample and hold an incoming analog signal at a sample-and-hold timing determined by a clock signal of a given frequency fc; and to transfer the analog signal from one step to another for delaying the signal for a period of time as desired.
In principle, the CCD is capable of allowing only a signal of a frequency band which is lower than 1/2 of the frequency fc of the above-stated clock signal to pass. In other words, the CCD allows only a signal of a frequency band which is lower than a Nyquist frequency to pass. In the actual use of the CCD, the signal frequency which can pass the CCD becomes lower than the Nyquist frequency and is, for example, fc/3, because of the sample-and-hold aperture, the characteristic of a band limiting filter which the signal must pass before the CCD and that of a clock signal removing filter to be arranged to remove the clock signal after the signal is output from the CCD.
During recent years, video tape recorders have come to be arranged to give a picture with a higher quality. As a result, the video signal is required to have a wider frequency band. To meet this trend, the above-stated use of the CCD requires that the frequency fc of the clock signal be raised for the wide band video signal. However, it is difficult at present to raise the clock signal frequency fc up to a value higher than 14 MHz or thereabout for the CCD. Besides, an attempt to raise the clock signal frequency fc is apt to result in an increase in the electric energy consumption and generation of noise components.